The patents listed 1-4 below are related recent technology.
1) Japan patent published 21841/78. This is technology devised to allow only low-level information from the stereo signal source to reach the listener. PA0 2) Japan patent early disclosure 107794/83. This is technology that achieves a sense of sound pressure by sending mechanical vibrations to tissue in the head and face. PA0 3) Japan patent early disclosure utility model 103909/77. This is a method for sending mechanical vibrations directly to the body. PA0 4) Insulated speaker - biaural. This is a method of stereo reproduction that eliminates crosstalk between the right and let signals by means of a sound arresting device placed at the center position of the listener.
Below, (a)-(e), are listed disadvantages with the technology described above.
(a) The listener to stereo sound reproduction is usually within a few meters distance of the speakers. Subsequently, the balance of sound pressure that the listener experiences is from a state of immediate proximity to the sound. This differs greatly from sounds encountered in nature or in a concert situation.
Most program sources are sounds signifying a distant source.
Therefore, there is often a gap between the body's awareness and the experience of the ear. This gap is responsible for the undesirable effect of a "floating" orientation. (Music listened to over headphones present the most extreme instance of the phenomenon.)
For the above reason it is impossible to achieve a stable and earthbound sound experience through the existing reproduction technology.
(b) Regardless of the nature of the program source, it is possible for the listener of a conventional stereo reproduction to clearly identify the location of the speakers. A particular reverberation is created at the listener's head according to the angle at which the sound penetrates. As long as this sound enters the ear, it is easy for the listener to recognize the sound source. Especially in cases such as conventional stereo reproduction, in which the direction of the sound source is simple to describe, this cranial reflection is very strong.
In the above manner, the listener hears stereo superfluous information. Because of the gap that has existed between the genuine image and the "ghost images" from the program source, stereo listeners have always been forced to listen to a peculiarly artificial type of reproduced sound.
Further, even when a biaural program source is used, the cranial reflection effect kills the orientation information included in the biaural system.
Invention (1) described above has the drawback that its effects are negated unless the position, orientation and angle of the head are kept fixed.
(c) It is possible to induce an effect of greater distance from the sound source by increasing the number of speakers, but at the same time, the distance between speakers is necessarily reduced, resulting in greater interference between speakers, increasing distortion. This distortion also kills biaural orientation information, making the enjoyment of biaural program sources impossible.
Japan patent early disclosure 107794/83 and Japan patent utility model 103909/77 contain technology that allows the sensation of sound pressure with headphones and closely-placed speakers, but inasmuch as they apply vibrations directly to the skin, their effect is unnatural.
(d) It is difficult to gain acoustical effects from directly in front of or directly behind the listener through biaural reproduction. This is because it is necessary for the dummy heads used at the time of creation of the program source to be of the same form as the head of the listener. But people have heads of all shapes. For this reason, it was difficult to accept the biaural method as satisfactory for general use.
(e) The present methods of reproduction function with the aid of room acoustics. Yet, as the users' rooms may vary, so will the sound quality. In the traditional methods, therefore, the true image of the program source's creator is not given the respect it is due. What is needed is a reproduction technique that does not depend on reverberation.